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[PATCH] vhost: Track descriptor chain in private at SVQ
From: |
Eugenio Pérez |
Subject: |
[PATCH] vhost: Track descriptor chain in private at SVQ |
Date: |
Tue, 12 Apr 2022 17:52:31 +0200 |
Only the first one of them were properly enqueued back.
While we're at it, harden SVQ: The device could have access to modify
them, and it definitely have access when we implement packed vq. Harden
SVQ maintaining a private copy of the descriptor chain. Other fields
like buffer addresses are already maintained sepparatedly.
Fixes: 100890f7ca ("vhost: Shadow virtqueue buffers forwarding")
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
hw/virtio/vhost-shadow-virtqueue.h | 6 ++++++
hw/virtio/vhost-shadow-virtqueue.c | 27 +++++++++++++++++++++------
2 files changed, 27 insertions(+), 6 deletions(-)
diff --git a/hw/virtio/vhost-shadow-virtqueue.h
b/hw/virtio/vhost-shadow-virtqueue.h
index e5e24c536d..c132c994e9 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -53,6 +53,12 @@ typedef struct VhostShadowVirtqueue {
/* Next VirtQueue element that guest made available */
VirtQueueElement *next_guest_avail_elem;
+ /*
+ * Backup next field for each descriptor so we can recover securely, not
+ * needing to trust the device access.
+ */
+ uint16_t *desc_next;
+
/* Next head to expose to the device */
uint16_t shadow_avail_idx;
diff --git a/hw/virtio/vhost-shadow-virtqueue.c
b/hw/virtio/vhost-shadow-virtqueue.c
index b232803d1b..a2531d5874 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -138,6 +138,7 @@ static void vhost_vring_write_descs(VhostShadowVirtqueue
*svq, hwaddr *sg,
for (n = 0; n < num; n++) {
if (more_descs || (n + 1 < num)) {
descs[i].flags = flags | cpu_to_le16(VRING_DESC_F_NEXT);
+ descs[i].next = cpu_to_le16(svq->desc_next[i]);
} else {
descs[i].flags = flags;
}
@@ -145,10 +146,10 @@ static void vhost_vring_write_descs(VhostShadowVirtqueue
*svq, hwaddr *sg,
descs[i].len = cpu_to_le32(iovec[n].iov_len);
last = i;
- i = cpu_to_le16(descs[i].next);
+ i = cpu_to_le16(svq->desc_next[i]);
}
- svq->free_head = le16_to_cpu(descs[last].next);
+ svq->free_head = le16_to_cpu(svq->desc_next[last]);
}
static bool vhost_svq_add_split(VhostShadowVirtqueue *svq,
@@ -333,13 +334,22 @@ static void
vhost_svq_disable_notification(VhostShadowVirtqueue *svq)
svq->vring.avail->flags |= cpu_to_le16(VRING_AVAIL_F_NO_INTERRUPT);
}
+static uint16_t vhost_svq_last_desc_of_chain(const VhostShadowVirtqueue *svq,
+ uint16_t num, uint16_t i)
+{
+ for (uint16_t j = 0; j < num; ++j) {
+ i = le16_to_cpu(svq->desc_next[i]);
+ }
+
+ return i;
+}
+
static VirtQueueElement *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
uint32_t *len)
{
- vring_desc_t *descs = svq->vring.desc;
const vring_used_t *used = svq->vring.used;
vring_used_elem_t used_elem;
- uint16_t last_used;
+ uint16_t last_used, last_used_chain, num;
if (!vhost_svq_more_used(svq)) {
return NULL;
@@ -365,7 +375,10 @@ static VirtQueueElement
*vhost_svq_get_buf(VhostShadowVirtqueue *svq,
return NULL;
}
- descs[used_elem.id].next = svq->free_head;
+ num = svq->ring_id_maps[used_elem.id]->in_num +
+ svq->ring_id_maps[used_elem.id]->out_num;
+ last_used_chain = vhost_svq_last_desc_of_chain(svq, num, used_elem.id);
+ svq->desc_next[last_used_chain] = svq->free_head;
svq->free_head = used_elem.id;
*len = used_elem.len;
@@ -540,8 +553,9 @@ void vhost_svq_start(VhostShadowVirtqueue *svq,
VirtIODevice *vdev,
svq->vring.used = qemu_memalign(qemu_real_host_page_size, device_size);
memset(svq->vring.used, 0, device_size);
svq->ring_id_maps = g_new0(VirtQueueElement *, svq->vring.num);
+ svq->desc_next = g_new0(uint16_t, svq->vring.num);
for (unsigned i = 0; i < svq->vring.num - 1; i++) {
- svq->vring.desc[i].next = cpu_to_le16(i + 1);
+ svq->desc_next[i] = cpu_to_le16(i + 1);
}
}
@@ -574,6 +588,7 @@ void vhost_svq_stop(VhostShadowVirtqueue *svq)
virtqueue_detach_element(svq->vq, next_avail_elem, 0);
}
svq->vq = NULL;
+ g_free(svq->desc_next);
g_free(svq->ring_id_maps);
qemu_vfree(svq->vring.desc);
qemu_vfree(svq->vring.used);
--
2.27.0
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